Eagle 4
You posed a question whether a Noob could be made as a Biplane.

Well, only a few pages back (page 160, Post # 2394) a very clever builder, RC Newbieoz has already done it and it flies great I beleive. You'll be able to follow his progress with specs and videos he made.

Eagle 4
You posed a question whether a Noob could be made as a Biplane.

Well, only a few pages back (page 160, Post # 2394) a very clever builder, RC Newbieoz has already done it and it flies great I beleive. You'll be able to follow his progress with specs and videos he made.

He's had a lot of praise about the 'fantastic look' of his model

Hope this is helpful
Geoff

Thanks for the compliment Geoff. I posted dimensions and pictures at post #2491.

Was the spar glued in? A spar that is glued in place will be 3 to 5 times stronger than a dowel that is just slipped in place. A spar that isn't glued in depends on the spar itself for 100% of its strength, a spar that is glued in full length becomes part of a much larger assembly working together to provide the strength. Basic engineering 101.

Having said what I did, I'm always receptive to evidence to the contrary. An assertion like "3 to 5 times stronger" from basic engineering 101 seems to speak from a published reference. Fixating things for strength like spars appeals to a general sense of physics, I admit, but I can't reconcile what specific spanwise forces would contribute to breaking the spar but that glue would resist. Can you point to a reference that elaborates on that?

The weight shift trike I once owned, like every one I've encountered, has a spar that is fixed only at the tips, mostly to allow the movement of the wing structure (nylon fabric with aluminum rib-like formers) over the spar to permit redistribution of the forces. It's not a perfect analogy but it's at least a premise for considering non-fixated spars.

I think the truth here might be a synthesis of Wingman26 and Templeton89, where gluing in the spar may add some nonspecific stiffness to the spar+foamwing assembly except where there's no foam to contribute strength at all: at the wing joint. And that joint is of course the fulcrum of the wing folding moment and most likely spot to break under any circumstances.

That's maybe a little heavy than my usual Axons by about 150g, but not bad. Maybe you have chunky landing gear or a bigger battery on it? If if flies like you want it to then it's pretty good in my book.

No I think a lot of my extra weight comes from the fiberglass rod I have in place of that wood one that kept breaking hah! I also had to add some extra weight to the nose to get it to balance right. (I don't have a camera on there yet) For my next one I think I definitely will be trying to build a lightweight version. Can you give me a number to shoot for in Grams? (is that what I should be using instead of lbs?)

Jhiggy, I've been using 5/16 square basswood or poplar spars and have only broken one on a horrendous crash. Be careful not to get balsa. I noticed that the square sticks are much stronger than the round ones and happen to be much easier to work with.

It's not clear from your photos how your rudder servo is hooked up to the rudder. Would you please post a photo showing the top side of that connection, showing how that apparently vertical servo thrown translates into horizontal motion for the rudder?

It's not clear from your photos how your rudder servo is hooked up to the rudder. Would you please post a photo showing the top side of that connection, showing how that apparently vertical servo thrown translates into horizontal motion for the rudder?

Thanks!

thanks syzygyQ
here you go

Images

I attached a mock up of what I was trying to explain.
Imagine that in both scenarios red arrow represents the same amount of force. Second image shows a situation where 2 wings halves are joined by a spar, but not glued together (i.e. a folding wing)

I dont know exact names and terms, but it's same effect as you'd get with a phone
book - grab it by the ends and it will bend and flex all you want, grab it tightly down the middle and you can rip it apart without too much effort.

As far as I can see leverage, stiffness and distribution of force all take a part in this. Not sure gluing the spar vs sliding it in would make any difference

The point that I'm trying to make is that a spar that is glued to the entire wing acts as one cohesive unit. Looking at the images you attached, the photo on the right is an example that is doomed to failure by its very design, you show 2 units with a weak spot in the middle, it has a designed in failure point.

When the wing spar is glued to an Armin wing type construction, even the wing skin adds to the overall strength of the wing and spar, as long as the bond is continuous.

The example that Ed spoke about is another thing, the weight shift trikes he's talking about, the covering is never considered in the design for weight bearing. In most full size aircraft with an aluminum wing they have an aluminum spar that has the aluminum skin riveted to it, and there are extra reinforcements riveted to the center of the wing spar. Some of the new construction methods include an aluminum spar and aluminum skin, with the wing bonded (glued) to the wing spar instead of riveted. All those forces are calculated in the design phase.

........I dont know exact names and terms, but it's same effect as you'd get with a phone book - grab it by the ends and it will bend and flex all you want, grab it tightly down the middle and you can rip it apart without too much effort..........

Glue all those pages together and then try to tear it apart...... Good Luck!

There must be thousands of good ways to remedy this. Laying down tongue depressors and reaming in a barbeque skewer to lift up one side showed promise.

In the end I tried spreading DAP Drydex Spackling with a tongue depressor. It goes on pink and turns white when it's ready to be sanded (4 hours min / overnight best). Eyeballing it it looked OK so I passed on sanding -- if you do sand it, you can use the same sanding blocks we use to bevel our trailing wing tips. I covered the Spackled area with duct tape, including into the edges of the cable hole up top to reduce water damage risk.

This produced a level flat top and tight flying characteristics. DAP Drydex Spackle is sold at Home Depot. They also have a super fast 5 / 10 minute version. It costs around $7-. You go through a surprising amount of it, but still, a small tub should be good for a half dozen medium sized surface build up jobs. It has a kind of firmness while at the same time being crumbly -- if it's well packed it stays firm and holds its shape. It's designed to be painted, which as I understand can seal it. We'll see if the duct tape binding wrapped around it will work, or if it will disintegrate, and if so how fast.

I've been advised that it's also great for filling in cracks and dings on airplanes in cases where looks matter, such as perhaps some of the neat scale style planes some of the guys here have been making.

Having said what I did, I'm always receptive to evidence to the contrary. An assertion like "3 to 5 times stronger" from basic engineering 101 seems to speak from a published reference. Fixating things for strength like spars appeals to a general sense of physics, I admit, but I can't reconcile what specific spanwise forces would contribute to breaking the spar but that glue would resist. Can you point to a reference that elaborates on that?

I think he means that with the spar glued in the foam-spar-foam sandwitch forms an I beam structure, it is stronger because it is now a relatively 'tall' beam. If the components coudl slide over one another, it would only be as stiff as the stiffest component. Once they're connected together, the top needs to compress and the bottom stretch in order for it to bend upward, hence adding to the stiffness of the spar, and resisting bending so far that it breaks.

PS I glued the spar into my Noob, but it came loose and fell out after landing. It was noticeably stiffer when the glue was still in place, the wing now has wrinkles in the top center section. Might be all those snap rolls I do (-:

There must be thousands of good ways to remedy this. Laying down tongue depressors and reaming in a barbeque skewer to lift up one side showed promise.

In the end I tried spreading DAP Drydex Spackling with a tongue depressor. It goes on pink and turns white when it's ready to be sanded (4 hours min / overnight best). Eyeballing it it looked OK so I passed on sanding -- if you do sand it, you can use the same sanding blocks we use to bevel our trailing wing tips. I covered the Spackled area with duct tape, including into the edges of the cable hole up top to reduce water damage risk.

This produced a level flat top and tight flying characteristics. DAP Drydex Spackle is sold at Home Depot. They also have a super fast 5 / 10 minute version. It costs around $7-. You go through a surprising amount of it, but still, a small tub should be good for a half dozen medium sized surface build up jobs. It has a kind of firmness while at the same time being crumbly -- if it's well packed it stays firm and holds its shape. It's designed to be painted, which as I understand can seal it. We'll see if the duct tape binding wrapped around it will work, or if it will disintegrate, and if so how fast.

I've been advised that it's also great for filling in cracks and dings on airplanes in cases where looks matter, such as perhaps some of the neat scale style planes some of the guys here have been making.

I'm glad you mentions this because I have the exact same issue. I was planning on using some foam to level it out or some hot glue so the wing stays level.

[QUOTE=Wingman26;24169206]The point that I'm trying to make is that a spar that is glued to the entire wing acts as one cohesive unit. Looking at the images you attached, the photo on the right is an example that is doomed to failure by its very design, you show 2 units with a weak spot in the middle, it has a designed in failure point.

OK, I think we're close to home. So it's agreed that stiffness = strength if it can be applied uniformly across the entire wing structure, and that a good way to do that is to affix the spar inside the wing. But for joined sections you lose that unitary strength thing due to the discontinuity in the foam and paper, so that does create a very high stress point right where you don't want it, and it does indeed as you say put all the force on the spar alone. So I would assert that if the spar becomes the bearer of all the forces then better to allow it to flex in a natural, catenary way as to distribute those forces than to concentrate all the force on one discrete spot. This can only happen if the spar is not glued in.

So the hierarchy of preference would be something like:

1. fixed spar, continuous foam and paper (when possible)
2. fixed spar with a reinforcement (tube over the center of spar, secondary spar, etc.) with discontinuous foam and paper
3. floating spar when no reinforcement or continuous foam and paper is possible.

I believe we were all kind of talking about two slightly different facets of this situation, but certainly it's important to consider everything.

My recommendation is to get some carbon fiber! Barring that I'd put a 6" aluminum tubing sleeve over the center of the spar, at the wing joint. What else are y'all using for this?